The objective of this proposal is to analyze the interrelationships of three fundamental cellular processes: 1. differentiation; 2. regulation of cell replication and 3. induction of cell division. As a model the developing submandibular gland of rat will be used in which DNA synthesis and cell division can be induced by the administration of isoproterenol. The postnatal differentiation of the gland will be analyzed with reference to the development of the adenyl cyclase-cyclic AMP-Beta-arenergic receptor system, to the synthesis of specific secretory proteins and to the surface speicalization of the acinar cells. In addition to assays of adenyl cyclase and phosphodiesterase activites and the concentration of cyclic AMP in the developing gland of control and isoproterend-treated rats, electron microscopic cytochemical and immunocytochemical techniques will be adapted to localize adenyl cyclase in the membrane of the acinar cells. The surface morphology of isolated acinar cells will be investigated with the scanning electron microscope. The differentiation of acinar cells will be correlated with the postnatal proliferation of acinar cells and with the induction DNA synthesis by isoproterenol in the same cells. DTX* ZO-33249-2*